In recent years, printed-circuit boards each comprising a printed-wiring board and a number of electronic components mounted on the board are used in increasing numbers, in electronic apparatuses such as personal computers. Generally, a printed-wiring board has a conductor pattern including a number of connection pads. Electronic components are mounted on the printed-wiring board, with their connection terminals soldered to the connection pads.
Recently, electronic apparatuses are made smaller and designed to have better performance. Printed-circuit boards for use in these apparatuses must therefore be small and must acquire high performance.
The smaller a printed-circuit board, the smaller its area. Nonetheless, more electronic components must be mounted to achieve higher performance. There is a limit to the density at which electronic components can be mounted. Thus it is difficult, in some cases, to mount all required components on the printed-wiring board. If so, it is impossible to miniaturize the printed-circuit board any more.